Merge mining is the only solution that makes sense here but there is no need to create a new coin or even a token (it would be useless) since there are altcoins out there that can and are already being merge mined by bitcoin miners providing them with additional revenue.

Another viable and possible better solution is to increase the capacity. After all in the far future the miners' revenue would come from fees. With a higher capacity the blocks would be able to contain more transactions and that translates into a higher fee sum therefore a higher revenue.